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Nicholas Wei and Paul Banaszkiewicz
fall onto her right hip. The anaesthetist is concerned about her anaesthetic risk for surgery. She
has mildly deranged clotting and LFTS results.
The most appropriate choice of management
would be
A. Bipolar cemented hemiarthroplasty hip
B. Cannulated screw fixation
C. Cemented total hip arthroplasty
D. Monopolar cemented hemiarthroplasty
E. Two-hole dynamic hip screw (DHS)
Figure 5.7
Anteroposterior
(AP) radiographs
femur
15. You see and list a 76-year-old female for a left
total hip arthroplasty. She has moderate
Parkinson’s disease.
The most appropriate option to reduce her
dislocation risk would be
A. 20° lipped liner
B. Captive cup
C. Change from a normal posterior approach to
the hip to an anterolateral Hardinge approach
D. Dual mobility cup
E. Use of a large femoral head (36mm if possible)
C. Convert to using a cement cup
D. Insert the next sized larger cup into the
acetabulum
E. Upsize and insert an uncemented TM revi-
sion cup
17. A patient with a large BMI (40) has been
referred to your clinic for a second opinion
regarding the need for THA. The first surgeon
who she met in clinic turned her down for THA
mentioning that risks of complications were too
significant with her large BMI.
With an increased BMI over 40 there is
A. Higher risk of revision for aseptic loosening
B. Higher risk of revision for mechanical failure
of the implant
C. Increased risk of mortality
D. Poorer functional outcome compared with
non-obese patients
E. Reduced improvement in pain scores com-
pared with non-obese patients
18. A 69-year-old male presents to ED complaining
of sudden onset of severe leg and hip pain. His
radiographs are shown in Figure 5.8.
The following statement is true
A. Calcar pivot is the most common mode of
failure
B. Mode 3 failure invol ves medial migration of
the proximal stem coupled with lateral migration of the distal stem tip
16. You are performing a hybrid hip replacement in
a 62-year-old patient with mild cognitive impairment. There is some concern about compliance
with post-operative instructions. The bone quality appears poor at surgery. The definitive cup is
a press fit design but is loose when impacted.
The most appropriate action is to
A. Add supplementary screw fixation
B. Change to a hydroxyapatite cup with screw
fixation
74
Figure 5.8 Anteroposterior (AP) radiographs pelvis
C. Mode 4 failure can be recognised early by
radiolucencies developing along the proximal
lateral cortex (convex) surface of the stem
D. The least common mode of failure is bending
cantilever failure
E. This radiograph demonstrates Gruen mode 2
failure
19. The most common mode of femoral stem fracture is
A. Bending cantilever (fatigue)
B. Calcar pivot
C. Medial midstem
D. Type 1b pistoning
E. Type 1a pistoning
Hip III Structured SBA
Figure 5.9 Anteroposterior (AP) radiograph pelvis
20. In theatre performing a cemented total hip
arthroplasty. The scrub nurse mixing the cement
mentions that they had recently been on a
‘cement training day’ organised by one of the
implant companies. She was unsure about the
difference between third- and fourth-generation
cementing techniques.
You mention
A. Fourth-generation cementing involves late
insertion of an implant into viscous cement
B. Fourth-generation cementing involves using
high pressure pulsed lavage
C. Fourth-generation involves using distal and
proximal centralisers to ensure an even
cement mantle
D. Fourth-generation techniques involve
improved stem designs
E. Third- and fourth-generation cementing
techniques are essentially the same procedure
21. A 72-year-old man returns to arthroplasty
follow-up clinic 1 year following cemented
THA. His AP radiograph is shown in Figure 5.9.
Concerning the X-ray appearance
A. Early removal is advisable in order to reduce
the risk of dislocation
B. It is a rare occurrence (<5%) after THA
C. Pathophysiology is an inappropriate differen-
tiation of pluripotent mesenchymal stem cells
D. Risk factors includes posterior approach
E. Very likely to result in lower Harris hip scores
22. Concerning heterotopic ossification (HO) after
total hip arthroplasty (THA), this is most likely
to occur in the following situation:
A. Ankylosing spondylitis
B. Head injury
C. Male sex
D. Ankylosed hip
E. Cementless prosthesis
23. Regarding Gruen’s mode of cemented femoral
stem failure
A. An initial mode Ia failure may progress into
mode II failure
B. Mode Ia is the most common cause of failure
C. Mode IV (bending cantilever) is rarely seen
D. Modes 1b, II and III are each seen in about
equal numbers
E. The modes of failure were based on a taper
slip femoral prosthesis
24. A 76-year-old female dislocates her THA 1 day
post-operatively in bed the next morning
following surgery. The THA was performed by
a trainee orthopaed ic surgeon although closely
supervised by their consultant.
The most likely reason for the dislocation
occurring would be
A. Component malalignment
B. Failure to remove osteophytes
C. Large, retained piece of cement in the hip
joint
75
Nicholas Wei and Paul Banaszkiewicz
D. Non-compliance with post-operative hip
precautions
E. Using a posterior approach to the hip and
failing to adequately repair the soft tissues
25. An 81-year-old man is admitted from the ED
with a dislocated left THA. He underwent the
surgery 3 weeks previously.
The strongest independent patient predictor of
early THA dislocation (within 40 days) is
A. Dementia
B. Depression
C. Lung disease
D. Parkinson’s disease
E. Spinal fusion
26. Regarding MoM resurfacing biomechanics.
Contact Patch to Rim Distance (CPRD) is most
influenced by
A. Arc of cover
B. Cup inclination angle
C. Cup version angle
D. Femoral head diameter
E. Head-cup clearance
B. Extraosseous extravascular (capsular) factors
C. Intraosseous arterial factors
D. Intraosseous extravascular factors
E. Intraosseous venous factors
29. A 43-year-old male presents to the orthopaedic
clinic with an 8-week history of severe left hip
pain. His radiographs are shown in Figure 5.10.
The most appropriate treatment would be
A. Bisphosphonates
B. Core decompression
C. Hip resurfacing
D. Total hip arthroplasty
E. Vascularised fibular graft
Figure 5.10
Anteroposterior
(AP) radiographs
pelvis
27. In the team brief before surgery the lead surgeon
is concerned about the dislocation risk in a
patient with cognitive impairment. The plan is
to use a large 36mm femoral head. The rationale
being that a larger femoral head will increase
jump distance.
Factors known to increase the jump distance
include
A. Decreased femoral head offset
B. Increase in cup anteversion angle
C. Increased abduction angle
D. Polyethylene liners with an offset
E. Smaller acetabular hemisphere
28. A 39-year-old male presents to the orthopaedic
clinic with severe acute onset of right hip pain of
8 w eeks’ duration. You suspect osteonecrosis. A
medical student in clinic has heard this condition
is due to a vascular disturbance in the femoral
head blood supply like a compartment syndrome
of bone.
The most likely vascular disturbance attributed
to a compartment syndrome of bone would be
A. Extraosseous arterial factors
30. During a total hip arthroplasty the senior sur-
geon asks the implant rep if his company’s
HXLPE is first- or second-generation. The
implant rep says he thinks it is secondgeneration and mumbles that it has been processed by 5 Mrad
The main difference between first- and secondgeneration HXLPE
A. First-generation annealed HXLPE contains
no residual free radicals
B. First-generation remelted HXLPE contains
elevated residual free radicals
C. Second-generation HXLPE involves a single
irradiation and remelting with addition of
vitamin E
D. Second-generation HXLPE involves sequen-
tial irradiation and annealing
E. Second-generation HXLPE involves sequen-
tial irradiation and remelting
76
Hip III Structured SBA
31. A 78-year-old female who underwent right THA
via a posterior approach is seen the next morning
with a dense painful foot drop.
The most appropriate initial management is
A. MRI scan
B. Nerve conduction studies
C. Physiotherapy and foot drop splint
D. Radiographs hip
E. Re-exploration of the hip
32. A 40-year-old man has been referred to the
orthopaedic clinic with a 6-week history of
(right) hip pain. The pain was unrelated to
trauma and was a severe, deep aching groin pain
worse at night. The patient has a limp with pain
on weight bearing and a positive Trendelenburg
sign. Radiographs of his hips are normal. An
MRI scan of his pelvis is shown (Figure 5.11).
Compared with standard UHMWPE HCLPE has
A. Decreased ductility
B. Increased fatigue strength
C. Increased fracture toughness
D. Increased tensile strength
E. Larger PE particles generated
34. A 48-year-old male with established severe osteo-
arthritis of the right hip is being listed for THA
in clinic. His neighbour has recommended using
a ceramic-on-ceramic hip replacement.
You mention that CoC bearing surfaces have
fallen out of popularity due to
A. Incidence of squeaking is now regarded as
being too high
B. Limited number of head and cup implant
options
C. Risk of catastrophic failure has not improved
with the fourth-generation Biolox delta
D. There are equivalent clinical results with a
ceramic and HCPLE bearing surface
combination
E. With limited healthcare budgets, the
increased cost for use has now become
prohibitive
Figure 5.11 T2 sagittal MRI pelvis
The most likely diagnosis is?
A. Bone marrow oedema syndrome
B. Infection (septic arthritis)
C. Osteochondromatosis
D. Osteonecrosis
E. Reflex sympathetic dystrophy
33. Surgical care practitioner is reviewing an AP
radiograph of a cemented THA in the arthroplasty follow-up clinic. The patient is doing
well but her radiographs suggest cup loosening.
There is no suggestion of infection. The cup has
been in 10 years and they are concerned about
the PE used.
35. You have performed an uncomplicated uncemented CoP THA on a 55-year-old male. The
patient was discharged at 2 days progressing well.
Medical staff shortages meant that his radiographs were not reviewed before discharge. You
review his post-operative radiographs after discharge (Figure 5.12).
The most important next step is
A. Arrange for a du ty of candour
B. Arrange for urgent clinic follow up
C. Ask the patient to attend the ED so that the
orthopaedic team on call can review the patient
D. Discuss the case at the next weekly MDT
E. Put protocols in place to make sure that all
radiographs are reviewed by the medical team
before patient discharge
36. A patient with an excessively anteverted uncemented cup returns early to clinic because of
concerns about the dislocation risk. His radiographs are shown in Figure 5.12. He is progressing well. You haven’t had a chance to discuss the
case at the next MDT due to the holiday period.
77
Nicholas Wei and Paul Banaszkiewicz
Figure 5.12 Anteroposterior (AP) pelvic radiographs
You recommend
A. Adopting a watch and wait policy for the hip
B. Ultrasound scan to look for iliopsoas
impingement
C. Prophylactic hip brace for 3 months
D. Making sure his physiotherapy is face to face
rather than just a telephone review
E. Revision to a dual motion cup liner
37. A 62-year-old male with known rheumatoid
arthritis is seen in clinic. He has severe end stage
co-existing right hip and knee arthritic pain with
a similar pain and functional disability level. He
asks that you proceed first with a TKA for him as
he thinks he is likely to recover more quickly
from the TKA.
The most appropriate management option is:
A. To arrange for a local anaesthestic/steroid
injection to be given to the knee to see how
he responds to the injection and therefore
how likely a TKA will relieve his knee pain
B. To arrange for a local anaesthestic/steroid injec-
tion to hip to gauge how severe his hip pain is
C. To arrange for a rheumatology review so that
his DMIARs medication can be reviewed and
changed if needed
D. To recommend that THA should be per-
formed before TKA
E. To take the patient’s wishes into account and
list for a TKA (Shared care process)
38. A 54-year-old female with known rheumatoid
arthritis has severe end stage co-existing right
hip and knee arthritic pain with a similar pain
and functional disability level. She has been listed
for THA but on the day of surgery asks whether
going ahead first with a TKA rather than THA
would be best.
All the following reasons are valid arguments
for proceeding with THA first EXCEPT
A. Adequate arc of hip motion is required for
deep knee flexion, which is often required for
successful TKA procedures
B. In patients with brittle rheumatoid arthritis
hip surgery is likely to be more straightforward than knee surgery and a patient’s confidence will be gained with performing
relatively easy surgery
C. It is best to resolve any knee pain that is
referred from the hip. At times even a TKA
can be delayed because of the pain relief
gained by replacing the hip
D. It is easier for a patient to exercise a hip above a
painful arthritic knee whereas it is difficult to
exercisea knee below a painful stiffarthritic hip
E. It makes sense to avoid twisting and torquing
a well-bal anced TKA while dislocating and
exposing a stiff hip for THA
39. You are performing THA in a 76-year-old male
and are keen to increase the femoral offset of the
implant to improve a weakened abductor function.
The options available to increase femoral offset
include
A. Decreasing the neck shaft angle
B. Decreasing the femoral neck length
C. Lateralising the femoral neck while concomi-
tantly decreasing the femoral neck length
78
Hip III Structured SBA
D. Use of a dual motion implant
E. Use of medialised acetabular liners
40. A 19-year-old ballet dancer presents with a snap-
ping sensation in the groin region.
On clinical examination, which of the following
manoeuvres will be most helpful in confirming
the diagnosis?
A. With the patient in the lateral position the
hip is flexed to 45° and the knee to 90°. The
pelvis is stabilised, and the flexed hip is
adducted
B. With the patient in the lateral position, the
hip is brought from flexion and adduction
into extension and abduction
C. With the patient supine, the hip is brought
from a position of flexion, abduction and
external rotation into extension, adduction
and internal rotation
D. With the patient supine, the hip is flexed to
90°, then add ucted and internal ly rotated
E. With the patient supine, the ipsilateral knee is
flexed to 90° and the hip is then extended,
adducted and externally rotated
41. When investigating the causative organism in
an infected THA which would be your preferred method?
A. Intraoperative frozen section
B. Intraoperative Gram stain
C. Percutaneous aspiration and culture
D. Polymerase chain reaction
E. Tissue culture of intraoperative biopsies
A. Use of a collarless femoral prosthesis
B. Use of a long posterior wall acetabular
component
C. Use of a monoblock femoral prosthesis
D. Use of a small femoral head
E. Use of hybrid components
44. An 80-year-old lady is being planned for a revi-
sion hip replacement for aseptic acetabular component loosening (Figure 5.13). You are
planning to revise the acetabular component to
an uncemented porous coated shell.
Which of the following statements is correct
regarding safe zones of the acetabulum?
A. Anterior-inferior quadrant has good bone stock
compared with posterior-superior quadrant
B. Anterior-superior quadrant is generally con-
sidered a safe zone for placement of acetabular screws
C. Risk of external iliac vessel injury is high with
posterior-inferior quadrant
D. Risk of injury to inferior gluteal and pudendal
vessels is high with posterior-inferior quadrant
E. Risk to superior gluteal vessels is high with
anterior superior quadrant
42. A 75-year-old patient presents with multiple episodes of dislocation following primary hip arthroplasty performed through a Hardinge approach.
Which of the following is the most appropriate
indication for useof a constrained acetabular liner?
A. Excessive anteversion of acetabular
component
B. Excessive anteversion of femoral stem
C. Femoral neck impingement
D. Gluteal muscle (abductor) deficiency
E. Revision hip surgery
43. Which of the following factors will result in the
greatest chance of an elective primary hip
arthroplasty dislocating?
Figure 5.13 Anteroposterior (AP) pelvis demonstrating loose
acetabular cup
45. A 59-year-old man is referred to the arthroplasty
clinic as a second opinion. He had Perthes disease as a child and had an uncemented THA
performed 2 years previously. He is complaining
of a clicking sensation around the hip,
79
Nicholas Wei and Paul Banaszkiewicz
Figure 5.14 Anteroposterior (AP) pelvis demonstrating left l THA
trochanteric discomfort, has a Trendelenburg
gait and hip pain with movements. His radiographs are shown in Figure 5.14.
The most likely cause for his pain is
A. Failure of osteointegration of the femoral stem
B. Leg length discrepancy
C. Proximal/distal femoral stem mismatch
D. Reduced femoral offset
E. Residue pain from Perthes disease
80
HIP III STRUCTURED SBA ANSWERS
1. Answer E. Using a cemented stem
An SBA to revise principles of stress shielding.
There is calcar reabsorption.
The radiograph is an example of subtle stress
shielding. This is the phenomenon of proximal
femoral bone density loss observed over time
in the presence of a solidly fixed implant.
Biomechanically, there is a decrease in the physiological stress to bone caused by the stiffer structure that shares its load.
Stem stiffness is the primary factor causing
stress shielding. The extent of porous coating has
some effect on stress shielding but is less important than stem stiffness.
The archetypal scenario of stress shielding in
THA is a large diameter stem that is made of CoCr alloy, has a round cylindrical shaft and has an
extensive porous coating.
Factors affecting stem stiffness include (1)
stem size, (2) metal choice and (3) stem geometry.
Stiffness increases in proportion to the fourth
power of the stem radius.
A stiffer material also increases stem stiffness.
Co-Cr has a higher mod ulus of elasticity than
titanium and is therefore stiffer.
Stems that are solid and round are stiffer.
Stem geometries that are less stiff include
hollow or tapered stems and stems that have slots
and flutes.
Hip III Structured SBA
acetabular component and the load imposed on
both the acetabular and femoral imp lants.
Excessive femoral offset has the potential to overload the femoral implant, to generate micromotion at the implant-bone interface and to cause
pain in the abductor muscles and the region of the
greater trochanter.
Failure to restore the femoral offset may lead
to excessive wear, fatigue, limping and/or hip
instability and an increased need for use of a
walking aid.
Charles MN et al. Soft tissue balancing of the
hip: the role of femoral offset restoration. J Bone
Joint Surg. 2004;86:1078–1088.
3. Answer B. Depend on stem stiffness
Although a well-fixed stem with stress shielding
does not affect implant survival it is prone to
fracture and revision of a stem with significant
stress shielding is difficult. Femoral cortical bone
is thin and more prone to damage during
extraction.
The stiffness of the material in a femoral stem
and the extent of porous coating covering the
component have been shown to contribute to
stress-shielding.
There is no increase in femoral osteolysis seen
in patients with stress shielding.
Risk factors for stress shielding includ e bone
quality, stem size, extent of porous coating, gender
and age.
2. Answer E. Trochanteric pain
The simplest and most frequently used measurement of femoral offset is the perpendicular
distance between the centre of the femoral head
and a line drawn down the centre of the femoral
shaft.
For the purpose of understanding the force
alterations that occur with alterations in offset,
the perpendicular distance from the line of action
of the abductor muscles to the centre of the femoral head is the most effective variable.
Femoral component offset depends on both
the length of the femoral neck and the neck-shaft
angle of the prosthesis.
Femoral offset is important because it controls
the tension and moment arm of the abductor
muscles, tension of the soft tissues, wear of the
Figure 5.15 Anteroposterior
(AP) radiograph right hip
demonstrating stress shielding
81
Nicholas Wei and Paul Banaszkiewicz
Clinical problems directly attributable to proximal femoral stress-related bone resorption have
not been reported to any significant degree in the
literature.
Engh Jr CA, Young AM, Engh Sr CA,
Hopper Jr RH. Clinical consequences of stress
shielding after porous-coated total hip arthroplasty. Clin. Orthop. 2003;417:157–163.
4. Answer B. Osteolysis
The patient’s radiographs demonstrate focal
osteolysis around the lesser trochanter. The major
differential diagnosis of focal osteolysis is generalised loosening, stress shielding, infection and
tumour. If there is rapid osteolysis or bone disintegration, then be suspicious of infection. It may
be necessary to culture joint aspirations. In infections, progression of bone loss is related to the
aggressiveness of the source organism. Tumour
will also show more aggressive destruction.
Osteolysis distal to the implant articulation is
explained as being due to direct access of joint fluid
and wear particles to the endosteal bone via the
bone-cement interface. In its most destructive form,
this pattern of focal endosteal osteolysis has been
labelled as an ‘aggressive granulomatous lesion’.
Focal osteolysis can be defined as a discrete
region of bone loss that occurs at the bone–
prosthesis or bone–cement interface and does
not conform to the prosthesis shape.
Osteolysis was defined as a localised or scalloped periprosthetic bone loss in order to distinguish it from loosening – which shows a linear or
more evenly extensively distributed bone loss
around the implant. Schmalzried et al. (1992)
studied hips with linear (diffuse) or lytic (localised) areas of periprosthetic bone loss. Although
the gross radiographic appearances of bone loss
were different, the histological appearance of
active bone resorption was similar. They suggested
that the radiological difference in bone loss may
be related to the local concentration of particulate
wear debris and the preferentia l flow within the
effective joint.
Several authors have demonstrated the potential for a passage to form at the stem–cement
interface. Joint fluid and particles are driven along
the interface by the high intra-articular pressures
generated during normal gait and reach the
cement–bone interface via defects in the cement
mantle. The resulting biological reaction can lead
to focal osteolysis in the presence of a well-fixed
cemented stem.
Cemented stems are considered definitely
loose when the component has migrated, a new
radiolucency at the cement–metal interface has
developed, the stem is fractured, or when the
cement mantle is fractured.
Many proposed mechanisms for focal femoral
osteolysis around cemented femoral components
have been put forward. These include stem micromotion (Charnley 1975), allergy to metal (Evans et
al. 1974), a tissue response to wear particles such as
polymethylmethacrylate(Horowitz et al.1993), high
density polyethylene (Jiranek et al. 1993) or metal
debris (Haynes 1993), a response to cytokines produced in the hip capsule and transportedin synovial
fluid (Nivbrant 1999) or as a tissue response to fluid
under pressure (van der Vis 1997).
Charnley J. Fracture of femoral prosthesis in
THR. Clin Orthop. 1975;111:105–120.
Evans E, Freeman M, Miller A, VernonRoberts B. Metal sensitivity as a cause of bone
necrosis and loosening of the prosthesis in TJR. J
Bone Joint Surg. 1974; 56-B:626–642.
Haynes D, Rogers S, Hay S, Pearsy M, Howie
D. The differences in toxicity and release of bone
resorbing mediators induced by titanium and CoCr -alloy wear particles. J Bone Joint Surg.
1993;75-A:825–834.
Horowitz S, Doty S, Lane J, Burnstein A.
Studies of the mechanism by which the mechanical failure of PMMA leads to bone resorption.J
Bone Joint Surg. 1993;75A:802–813.
Jiranek W, Machado M, Jasty M. Production
of cytokines around loosened cemented acetabular
components. J Bone Joint Surg. 1993;75-
A:863–879.
Nivbrant B, Karlsson K, Karrholm J.
Cytokine levels in synovial fluid from hips with
well functioning or loose prostheses. J Bone Joint
Surg. 1999;81-B:163–166.
Park JS et al. Focal osteolysis in total hip
replacement: CT findings. Skeletal Radiol.
2004;33:632–640.
Schmalzried TP, Jasty M, Harris WH.
Periprosthetic bone loss in total hip arthroplasty:
polyethylene wear debris and the concept of the
effective joint space. J Bone Joint Surg Am.
1992;74:849–863.
82
Hip III Structured SBA
Van Der Vis H, Marti R, Tigchelaar W,
Schuller H, Van Noorden C. Benign cellular
responses in rats to different wear particles in
intra-articular and intramedullary environments.
J Bone Joint Surg. 1997;79B:837– 843.
5. Answer B. CT scan
The patient’s hip symptoms are non-specific, not
disabling and short term. The lucency around the
proximal femoral component is a long-standing
feature and comparison should be made of previous radiographs if available to see progression of
the disease. In view of her advanced age and lack
of specific hip symptoms the best course of action
would be for a CT scan which would be useful for
the prediction and assessment of the nature and
extent of focal osteolysis.
The lesion is best managed conservatively
with yearly clinic review and serial radiographs
to see if the lesion is expanding and threatening
a periprosthetic fracture. However it would be a
brave decision based purely on plain radiographic
appearance to review the patient in a year without
any further investigations. Option D is a realistic
distractor with some debate as to whether to
schedule follow up at 6 months rather than
1 yearly.
Ordering a bone scan is a reasonable option
but not essential as radiographs do suggest only a
localised osteolysis and no widespread femoral
stem loosening. More generally a bone scan would
identify whether an area of osteolysis was more
widespread than anticipated or if the stem was
loose. It is likely her focal osteolysis is asymptomatic and very slowly progressive.
Any revision surgery would be a large undertaking in this elderly patient. A full revision may
be necessary as leaving the cup in situ may limit
the head size that can be used and so increasing
the risk for dislocation. If needed a full revision
with a dual motion acetabular component would
be a reasonable option.
Bone biopsy for suspected focal osteolysis
would show a foreign body reaction with multinucleated giant cells and monocyte macrophages.
Plain radiography is the cornerstone of evaluation
and has been used to determine the extent and
nature of focal osteolysis.
Beck RT, Illingworth KD, Saleh KJ. Review of
periprosthetic osteolysis in total joint arthroplasty:
an emphasis on host factors and future directions.
J Orthop Res. 2012;30:541–546.
Park JS et al. Focal osteolysis in total hip replace-
ment: CT findings. Skeletal Radiol. 2004;33:632–640.
6. Answer E. Remodelling of radial trabeculae
pattern
The fall should alert the reader to look for any
associated periprosthetic fracture or any otherpelvic
fracture such as a pubic rami or sacral fracture. The
patient has had a hybrid hip replacement performed
with the cup being uncemented. The SBA is testing
the reader ifthey are aware of radiographic signs ofa
stable acetabular uncemented cup fixation.
Moore et al. (2006) compared radiographic
appearances of bone ingrowth acetabular components with findings at revision surgery (Figure
5.18). They found five signs useful in determining
stable uncemented acetabular fixation that are:
Absence of radiolucent lines.
Presence of a superolateral buttress (Figure 5.19).
Medial bone stress-shielding (Figure 5.20).
Radial trabeculae (Figure 5.21).
Inferomedial buttress.
Ninety-seven per cent of cups with three or more
of these signs were stable at the time of revision
surgery whereas 83% of the cups with two or fewer
signs were loose.
In osseointegrated uncemented cups, redistri-
bution of load to the periphery of the bone–cup
interface results in the development of superolateral and inferomedial bone densities called buttresses. An osseointegrated uncemented cup exerts
tensile forces at the inferior region of the acetabulum, producing bone hypertrophy at that region.
Implantation of a device stiffer than the subchondral plate results in redistribution of forces to the
periphery of the ilium and away from the central
cancellous bone.
The decreased loading on the medial subchondral or retroacetabular bone becomes evident as
medial stress-shielding. This is secondary to a
decrease in the loading of the apical region of the
acetabulum when osseointegration has been successful superolaterally and inferomedially.
Abnormal shear and peak contact forces are
produced in an arthritic hip, resulting in medial
subchondral sclerosis. After an uncemented cup is
implanted, this sclerosis resolves and a trabecular
83
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